Transgenic impact Pigs fed a diet of genetically modified grain showed markedly higher stomach inflammation than pigs who dined on conventional feed, according to a new study by Australian and US researchers.

But other researchers question the methodology used to analyse the results, suggesting other factors may be at play.

The study adds to an intensifying public debate over the impact of genetically modified crops, which is increasingly being used around the world.

The study was published in the June issue of the peer-reviewed Journal of Organic Systems by researchers from Australia who worked with two veterinarians and a farmer in Iowa to study the pigs.

The study was conducted over 22.7 weeks using 168 newly weaned pigs in a commercial US piggery.

One group of 84 ate a diet that incorporated genetically modified (GM) soy and corn, and the other group of 84 pigs ate an equivalent non-GM diet. According to the study, the corn and soy feed was obtained from commercial suppliers and the pigs were reared under identical housing and feeding conditions.

The pigs were then slaughtered roughly five months later and autopsied by veterinarians who were not informed which pigs were fed on the GM diet and which were from the control group.

Researchers say there were no differences seen between pigs fed the GM and non-GM diets for feed intake, weight gain, mortality, and routine blood biochemistry measurements.

But those pigs that ate the GM diet had a higher rate of severe stomach inflammation - 32 per cent of GM-fed pigs compared to 12 per cent of non-GM-fed pigs. As well, GM-fed pigs had uteri that were 25 per cent heavier than non-GM fed pigs, the study's authors wrote.

The researchers say more long-term animal feeding studies need to be done.

Questionable numbers

Emeritus Professor Jock McLean of Swinburne University of Technology in Melbourne, says both the methodology used to extract and grade the pig's organs, as well as the statistical analysis is flawed.

McLean, who was a veterinary toxicologist at the University of Melbourne and has worked as a consultant in the field for the past 20 years, says the differences in uteri weight could be explained by the presence of fumonisins - a mycotoxin produced by fungi that forms on corn feed held in storage. Fumonisins are known to cause increased levels of oestrogen in pigs.

He points out that the study's analysis shows the level of fumonisins in the GM-feed were 3.0 parts per million, compared to 1.2 ppm in the non-GM-feed.

"You cannot rule out the fact that the higher uteri weight wasn't the result of this," says McLean.

He adds that the pigs were more than six months old, which meant some of them could have reached puberty, hence the changes in uteri weight.

Also of concern to McLean is the sudden change in the rate of stomach inflammation observed in the study. Overall, the pigs in showed the same rates of inflammation across all levels, and that the rates of mild and moderate inflammation were higher in the non-GM-fed pigs than the GM-fed pigs.

"It's only in the severe group that you get a difference in the GM-fed pigs and non-GM-fed pigs," says McLean. "You'd expect to get a few in the mild [group], a few more in the intermediate, and more in the serious. You'd get a graduation."

"In fact, I could argue that the GM-food is actually protecting against ulcers and the contamination with mycotoxins or fungal toxins is the reason why the uterine rates are slightly different."

Novel proteins

Biotech seeds are genetically altered to grow into plants that tolerate treatments of herbicide and resist pests, making producing crops easier for farmers. Some critics have argued for years that the DNA changes made to the transgenic plants engineer novel proteins that can be causing the digestive problems in animals and possibly in humans.

The companies that develop these transgenic crops, using DNA from other bacteria and other species, assert they are more than proven safe over their use since 1996.

CropLife International, a global federation representing the plant science industry, said more than 150 scientific studies have been done on animals fed biotech crops and to date, there is no scientific evidence of any detrimental impact.